The present invention relates to an analog circuit for a baseband modem associated with a predefined logic circuit and comprising members which effect electronic functions on electric signals including, for example, filtering, amplification, putting an analog delay into effect, comparisons, automatic equalization by means of a non-linear arrangement.
Such an analog circuit is disclosed in the publication "Commutation et Transmission", no. 1, 1985, which describes a "baseband modem operating in duplex over two wires". The modem is mainly comprised of a predefined logic circuit which provides the functions which are linked to transmission, to echo cancelation and to reception and have a plurality of passive and active bipolar circuits which provide the analog functions including amplification, filtering, putting an analog delay into effect, comparison and automatic equalization. Equalization in particular is obtained by means of a non-linear arrangement constituted by a high-pass filter whose cut-off frequency varies automatically by the action of diodes which short-circuit a capacitor to a certain extent. Such a modem has already a level of integration, however to still further improve its compactness and its reliability as well as to reduce its power consumption still more it is desirable for several analog functions to be combined in a CMOS integrated circuit which thus might be directly associated with the predefined logic circuit. At any rate, the integration of these analog functions poses obvious difficulties, more specifically as regards the impossiblity of realizing in CMOS technology the diodes which are necessary for the automatic equalization.
The invention has for its object to obviate these difficulties and proposes means to significantly reduce the volume and the electric power consumption and as a result thereof to improve the reliability and the reproducibility of such a modem, while reducing its cost.